Cunningham K W, Fink G R
Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Mol Cell Biol. 1996 May;16(5):2226-37. doi: 10.1128/MCB.16.5.2226.
The PMC1 gene in Saccharomyces cerevisiae encodes a vacuolar Ca2+ ATPase required for growth in high-Ca2+ conditions. Previous work showed that Ca2+ tolerance can be restored to pmc1 mutants by inactivation of calcineurin, a Ca2+/calmodulin-dependent protein phosphatase sensitive to the immunosuppressive drug FK506. We now report that calcineurin decreases Ca2+ tolerance of pmc1 mutants by inhibiting the function of VCX1, which encodes a vacuolar H+/Ca2+ exchanger related to vertebrate Na+/Ca2+ exchangers. The contribution of VCX1 in Ca2+ tolerance is low in strains with a functional calcineurin and is high in strains which lack calcineurin activity. In contrast, the contribution of PMC1 to Ca2+ tolerance is augmented by calcineurin activation. Consistent with these positive and negative roles of calcineurin, expression of a vcx1::lacZ reporter was slightly diminished and a pmc1::lacZ reporter was induced up to 500-fold by processes dependent on calcineurin, calmodulin, and Ca2+. It is likely that calcineurin inhibits VCX1 function mainly by posttranslational mechanisms. Activities of VCX1 and PMC1 help to control cytosolic free Ca2+ concentrations because their function can decrease pmc1::lacZ induction by calcineurin. Additional studies with reporter genes and mutants indicate that PMR1 and PMR2A, encoding P-type ion pumps required for Mn2+ and Na+ tolerance, may also be induced physiologically in response to high-Mn2+ and -Na+ conditions through calcineurin-dependent mechanisms. In these situations, inhibition of VCX1 function may be important for the production of Ca2+ signals. We propose that elevated cytosolic free Ca2+ concentrations, calmodulin, and calcineurin regulate at least four ion transporters in S. cerevisiae in response to several environmental conditions.
酿酒酵母中的PMC1基因编码一种在高钙条件下生长所必需的液泡Ca2+ATP酶。先前的研究表明，通过使钙调神经磷酸酶失活，可将Ca2+耐受性恢复至pmc1突变体，钙调神经磷酸酶是一种对免疫抑制药物FK506敏感的Ca2+/钙调蛋白依赖性蛋白磷酸酶。我们现在报告，钙调神经磷酸酶通过抑制VCX1的功能来降低pmc1突变体的Ca2+耐受性，VCX1编码一种与脊椎动物Na+/Ca2+交换体相关的液泡H+/Ca2+交换体。在具有功能性钙调神经磷酸酶的菌株中，VCX1对Ca2+耐受性的贡献较低，而在缺乏钙调神经磷酸酶活性的菌株中则较高。相反，钙调神经磷酸酶的激活增强了PMC1对Ca2+耐受性的贡献。与钙调神经磷酸酶的这些正向和负向作用一致，依赖于钙调神经磷酸酶、钙调蛋白和Ca2+的过程使vcx1::lacZ报告基因的表达略有降低，而pmc1::lacZ报告基因被诱导高达500倍。钙调神经磷酸酶可能主要通过翻译后机制抑制VCX1的功能。VCX1和PMC1的活性有助于控制胞质游离Ca2+浓度，因为它们的功能可以降低钙调神经磷酸酶对pmc1::lacZ的诱导。对报告基因和突变体的进一步研究表明，编码对Mn2+和Na+耐受性所需的P型离子泵的PMR1和PMR2A，也可能通过钙调神经磷酸酶依赖性机制在生理上响应高Mn2+和-Na+条件而被诱导。在这些情况下，抑制VCX1的功能对于Ca2+信号的产生可能很重要。我们提出，升高的胞质游离Ca2+浓度、钙调蛋白和钙调神经磷酸酶可响应几种环境条件调节酿酒酵母中至少四种离子转运体。
